1. Field of the Invention
The present invention generally relates to vehicles, and more particularly to a coasting deceleration control device and process for a vehicle having a driving system with a motor/generator and a transmission.
2. Background Art
In an automotive vehicle equipped with an ordinary automatic transmission having a plurality of gear ratio steps, coasting deceleration is affected by the amount of engine friction depending upon the accelerator position or whether braking is applied. Further, the engine friction can change depending on the number of revolutions of the engine that may be a function of the rotating speed of the engine or engine revolutions per minute (RPM). Shifting from a higher gear to a lower gear so that the engine rotates faster for the same speed of the wheels, is often referred to as down shifting. Further, the amount of force transmitted to a rear end portion of the transmission due to friction varies depending on the transmission gear ratio that is determined according to a shift schedule or a down shift schedule in the case of coasting deceleration.
Generally, coasting deceleration of a vehicle equipped with a stepped transmission is predetermined when the vehicle is designed. Accordingly, the range of coasting deceleration cannot be adjusted to satisfy various driving conditions. For example, if a driver feels that the coasting vehicle is decelerating too slowly, then the driver may downshift or use a lower gear range or deactivate an overdrive in order to increase the amount of coasting deceleration. However, it is difficult to for an ordinary automatic transmission to always perform provide coasting deceleration at a desired rate.
A vehicle equipped with a CVT (Continuously Variable Transmission) can very quickly detect the driver's intent to decelerate and can change a transmission gear ratio of the CVT, thereby adjusting the coasting deceleration to a desired level of drivability. Such features are exemplified in Japanese Patent Laid-Open Application No. 2003-74682, for example.